Method for making metal nanowires film

ABSTRACT

The disclosure relates to a method for making a metal nanowire film. The method includes applying a metal layer on a substrate; placing a carbon nanotube composite structure on the metal layer, wherein the carbon nanotube composite structure defines a number of openings and parts of the metal layer are exposed by the number of openings; dry etching the metal layer using the carbon nanotube composite structure as a mask; and removing the carbon nanotube composite structure. The carbon nanotube composite structure includes a carbon nanotube structure and a protective layer coated on the carbon nanotube structure. The carbon nanotube structure includes a number of carbon nanotubes arranged substantially along the same direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201510263855.8, filed on May 21, 2015, inthe China Intellectual Property Office, disclosure of which isincorporated herein by reference.

FIELD

The subject matter herein generally relates to nano materials andmethods for making the same, in particular, to metal nanowire films andmethods for making the same based on carbon nanotubes.

BACKGROUND

Transparent conductive film is attracting more and more attention inelectronic device field because of widely application.

The transparent conductive film includes indium tin oxide (ITO) layer,carbon nano tube (CNT) film, or metal mesh. Usually, the method formaking metal mesh is chemical etching which is complicated. The linewidth of the metal mesh is usually about tens of micrometers due to theprocess limitation. When the metal mesh is used in small size electronicdevice, such as mobile phone or tablet computer, the metal wires of themetal mesh are visible to the naked eye.

What is needed, therefore, is to provide a method for solving theproblem discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures, wherein:

FIG. 1 is a flowchart of one embodiment of a method for making a metalnanowire film on a surface of a substrate of one embodiment.

FIG. 2 is a cross-sectional view along line II-II of FIG. 1.

FIG. 3 is a Scanning Electron Microscope (SEM) image of a drawn carbonnanotube film of one embodiment.

FIG. 4 is an SEM image of an untwisted carbon nanotube wire of oneembodiment.

FIG. 5 is an SEM image of a twisted carbon nanotube wire of oneembodiment.

FIG. 6 is an SEM image of a carbon nanotube composite structure withcross-stacked drawn carbon nanotube films of one embodiment.

FIG. 7 is a transmission electron microscope (TEM) image of a singlecarbon nanotube coated by alumina (Al2O3) layer of one embodiment.

FIG. 8 is a SEM image of a drawn carbon nanotube film after lasertreating of one embodiment.

FIGS. 9-10 are SEM images of a metal nanowire film fabricated in example1.

FIG. 11 is a SEM image of metal nanowires of the metal nanowire filmfabricated in example 1.

FIG. 12 shows test results of transmittance and sheet resistance of themetal nanowire film fabricated in example 1.

FIG. 13 is a SEM image of a metal nanowire film fabricated in example 2.

FIG. 14 is a schematic view of the metal nanowire film fabricated inexample 2.

FIG. 15 is an enlarged view of part XV of metal nanowires bundle of themetal nanowire film of FIG. 14.

FIG. 16 is a SEM image of a metal nanowire film fabricated in example 3.

FIG. 17 is a schematic view of the metal nanowire film fabricated inexample 3.

FIG. 18 shows test results of transmittance and sheet resistance of themetal nanowire film fabricated in example 3.

FIG. 19 shows a relationship of sheet resistance under heating and timeof the metal nanowire film fabricated in example 4.

FIG. 20 shows a relationship of sheet resistance under heating andtemperature of the metal nanowire film fabricated in example 4.

FIG. 21 is a SEM image of a metal nanowire film fabricated in example 5.

FIG. 22 shows test results of transmittance and sheet resistance of themetal nanowire film fabricated in example 5.

FIG. 23 is a SEM image of a metal nanowire film fabricated in example 6.

FIG. 24 shows test results of transmittance and sheet resistance of themetal nanowire film fabricated in example 6.

FIG. 25 is a SEM image of a metal nanowire film fabricated in example 7.

FIG. 26 shows test results of transmittance and sheet resistance of themetal nanowire film fabricated in example 7.

FIG. 27 is a SEM image of a metal nanowire film fabricated in example 8.

FIG. 28 shows test results of transmittance and sheet resistance of themetal nanowire film fabricated in example 8.

FIG. 29 shows a relationship of sheet resistance under heating andtemperature of the metal nanowire film fabricated in example 9.

FIG. 30 shows a relationship of sheet resistance under heating and timeof the metal nanowire film fabricated in example 9.

FIG. 31 shows a relationship of sheet resistance under heating andtemperature of the metal nanowire film fabricated in example 10.

FIG. 32 shows a relationship of sheet resistance under heating and timeof the metal nanowire film fabricated in example 10.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures and components have notbeen described in detail so as not to obscure the related relevantfeature being described. The drawings are not necessarily to scale andthe proportions of certain parts may be exaggerated to better illustratedetails and features. The description is not to be considered aslimiting the scope of the embodiments described herein.

Several definitions that apply throughout this disclosure will now bepresented.

The term “coupled” is defined as connected, whether directly orindirectly through intervening components, and is not necessarilylimited to physical connections. The connection can be such that theobjects are permanently connected or releasably connected. The term“substantially” is defined to be essentially conforming to theparticular dimension, shape or other word that substantially modifies,such that the component need not be exact. The term “comprising” means“including, but not necessarily limited to”; it specifically indicatesopen-ended inclusion or membership in a so-described combination, group,series and the like. It should be noted that references to “an” or “one”embodiment in this disclosure are not necessarily to the sameembodiment, and such references mean at least one.

References will now be made to the drawings to describe, in detail,various embodiments of the present metal nanowire films and methodsmaking the same based on carbon nanotubes.

Referring to FIGS. 1-2, a method for making a metal nanowire film 104 ofone embodiment includes the following steps:

step (S10), applying a metal layer 102 on a surface 101 of a substrate100;

step (S11), providing a carbon nanotube composite structure 110, whereinthe carbon nanotube composite structure 110 defines a plurality ofopenings 116 and includes a carbon nanotube structure 112 and aprotective layer 114 coated on the carbon nanotube structure 112, andthe carbon nanotube structure 112 includes a plurality of carbonnanotubes arranged substantially along the same direction;

step (S12), placing the carbon nanotube composite structure 110 on asurface of the metal layer 102, wherein parts of the metal layer 102 areexposed by the plurality of openings 116;

step (S13), forming the metal nanowire film 104 on the substrate 100 bydry etching the metal layer 102 using the carbon nanotube compositestructure 110 as a mask; and step (S14), removing the carbon nanotubecomposite structure 110.

In step (S10), the substrate 100 can be a curved or planar sheetconfigured to support metal nanowire film 104. The substrate 100 can betransparent or opaque. The substrate 100 can be flexible or rigid. Thesubstrate 100 can be made of rigid materials such as silicon wafer,ceramic, glass, quartz, diamond, metal oxide, plastic or any othersuitable material. The substrate 100 can be made of flexible materialssuch as polycarbonate (PC), polymethyl methacrylate acrylic (PMMA),polyethylene terephthalate (PET), polyether polysulfones (PES),polyvinyl polychloride (PVC), benzocyclobutenes (BCB), polyesters,polyimide (PI), polyethylene (PE), acrylonitrile-butadiene-styrenecopolymer (ABS), polyamide (PA), polybutylene terephthalate (PBT),acrylic resins, or mixture thereof. The mixture can be PC/ABS, PC/PBT,PC/PET, or PC/PMMA. The substrate 100 can also be a printed-wiring board(PWB). The light transmittance of the substrate 100 can be greater than75%, such as greater than 90%. In one embodiment, the substrate 100 is aplanar glass plate.

The material of the metal layer 102 is not limited and can be gold,silver, copper, iron, aluminum, nickel or chromium. The metal layer 102can be applied on the substrate 100 by a deposition method such aselectron beam evaporation, magnetron sputtering or atomic layerdeposition. The metal layer 102 can be patterned by dry etching. Thethickness of the metal layer 102 can be less than 100 nanometers, suchas less than 50 nanometers. In one embodiment, the metal layer 102 is agold film with a thickness of 10 nanometers and coated on entire surface101 of the substrate 100.

In step (S11), the carbon nanotube structure 112 is a free-standingstructure. The term “free-standing structure” includes that the carbonnanotube structure 112 can sustain the weight of itself when it ishoisted by a portion thereof without any significant damage to itsstructural integrity. Thus, the carbon nanotube structure 112 can besuspended by two spaced supports.

The plurality of carbon nanotubes can be single-walled carbon nanotubes,double-walled carbon nanotubes, or multi-walled carbon nanotubes. Thelength and diameter of the plurality of carbon nanotubes can be selectedaccording to need. The diameter of the single-walled carbon nanotubescan be in a range from about 0.5 nanometers to about 10 nanometers. Thediameter of the double-walled carbon nanotubes can be in a range fromabout 1.0 nanometer to about 15 nanometers. The diameter of themulti-walled carbon nanotubes can be in a range from about 1.5nanometers to about 50 nanometers. In one embodiment, the length of thecarbon nanotubes can be in a range from about 200 micrometers to about900 micrometers.

The plurality of carbon nanotubes are orderly arranged to form anordered carbon nanotube structure. The plurality of carbon nanotubesextend along a direction substantially parallel to the surface of thecarbon nanotube structure 112. The term ‘ordered carbon nanotubestructure’ includes, but is not limited to, a structure wherein theplurality of carbon nanotubes are arranged in a consistently systematicmanner, e.g., the plurality of carbon nanotubes are arrangedapproximately along the same direction.

The carbon nanotube structure 112 defines a plurality of apertures. Theaperture extends throughout the carbon nanotube structure 112 along thethickness direction thereof. The aperture can be a hole defined byseveral adjacent carbon nanotubes, or a gap defined by two substantiallyparallel carbon nanotubes and extending along axial direction of thecarbon nanotubes. The hole shaped aperture and the gap shaped aperturecan exist in the carbon nanotube structure 112 at the same time.Hereafter, the size of the aperture is the diameter of the hole or widthof the gap. The sizes of the apertures can be different. The averagesize of the apertures can be in a range from about 10 nanometers toabout 500 micrometers. For example, the sizes of the apertures can beabout 50 nanometers, 100 nanometers, 500 nanometers, 1 micrometer, 10micrometers, 80 micrometers, or 120 micrometers.

The carbon nanotube structure 112 can include at least one carbonnanotube film, at least one carbon nanotube wire, or combinationthereof. In one embodiment, the carbon nanotube structure 112 caninclude a single carbon nanotube film or two or more carbon nanotubefilms stacked together. Thus, the thickness of the carbon nanotubestructure 112 can be controlled by the number of the stacked carbonnanotube films. The number of the stacked carbon nanotube films can bein a range from about 2 to about 100. For example, the number of thestacked carbon nanotube films can be 10, 30, or 50. In one embodiment,the carbon nanotube structure 112 is formed by folding a single carbonnanotube wire. In one embodiment, the carbon nanotube structure 112 caninclude a layer of parallel and spaced carbon nanotube wires. Also, thecarbon nanotube structure 112 can include a plurality of carbon nanotubewires crossed or weaved together to form a carbon nanotube net. Thedistance between two adjacent parallel and spaced carbon nanotube wirescan be in a range from about 0.1 micrometers to about 200 micrometers.In one embodiment, the distance between two adjacent parallel and spacedcarbon nanotube wires is in a range from about 10 micrometers to about100 micrometers. The gap between two adjacent substantially parallelcarbon nanotube wires is defined as the apertures. The size of theapertures can be controlled by controlling the distance between twoadjacent parallel and spaced carbon nanotube wires. The length of thegap between two adjacent parallel carbon nanotube wires can be equal tothe length of the carbon nanotube wire. It is understood that any carbonnanotube structure described can be used with all embodiments.

In one embodiment, the carbon nanotube structure 112 includes at leastone drawn carbon nanotube film. The drawn carbon nanotube film can bedrawn from a carbon nanotube array that is able to have a film drawntherefrom. The drawn carbon nanotube film includes a plurality ofsuccessive and oriented carbon nanotubes joined end-to-end by van derWaals attractive force therebetween. The drawn carbon nanotube film is afree-standing film. Referring to FIG. 3, each drawn carbon nanotube filmincludes a plurality of successively oriented carbon nanotube segmentsjoined end-to-end by van der Waals attractive force therebetween. Eachcarbon nanotube segment includes a plurality of carbon nanotubesparallel to each other, and combined by van der Waals attractive forcetherebetween. As can be seen in FIG. 3, some variations can occur in thedrawn carbon nanotube film. The carbon nanotubes in the drawn carbonnanotube film are oriented along a preferred orientation. The drawncarbon nanotube film can be treated with an organic solvent to increasethe mechanical strength and toughness and reduce the coefficient offriction of the drawn carbon nanotube film. A thickness of the drawncarbon nanotube film can range from about 0.5 nanometers to about 100micrometers. The drawn carbon nanotube film defines a plurality ofapertures between adjacent carbon nanotubes.

The carbon nanotube structure 112 can include at least two stacked drawncarbon nanotube films. In other embodiments, the carbon nanotubestructure 112 can include two or more coplanar carbon nanotube films,and can include layers of coplanar carbon nanotube films. Additionally,when the carbon nanotubes in the carbon nanotube film are aligned alongone preferred orientation (e.g., the drawn carbon nanotube film), anangle can exist between the orientation of carbon nanotubes in adjacentfilms, whether stacked or adjacent. Adjacent carbon nanotube films canbe combined by only the van der Waals attractive force therebetween. Anangle between the aligned directions of the carbon nanotubes in twoadjacent carbon nanotube films can range from about 0 degrees to about90 degrees. When the angle between the aligned directions of the carbonnanotubes in adjacent stacked drawn carbon nanotube films is larger than0 degrees, a plurality of micropores is defined by the carbon nanotubestructure 112. In one embodiment, the carbon nanotube structure 112 hasthe aligned directions of the carbon nanotubes between adjacent stackeddrawn carbon nanotube films at 90 degrees. Stacking the carbon nanotubefilms will also add to the structural integrity of the carbon nanotubestructure 112.

The carbon nanotube wire can be untwisted or twisted. Treating the drawncarbon nanotube film with a volatile organic solvent can form theuntwisted carbon nanotube wire. Specifically, the organic solvent isapplied to soak the entire surface of the drawn carbon nanotube film.During the soaking, adjacent parallel carbon nanotubes in the drawncarbon nanotube film will bundle together, due to the surface tension ofthe organic solvent as it volatilizes, and thus, the drawn carbonnanotube film will be shrunk into an untwisted carbon nanotube wire.Referring to FIG. 4, the untwisted carbon nanotube wire includes aplurality of carbon nanotubes substantially oriented along the samedirection (i.e., a direction along the length of the untwisted carbonnanotube wire). The carbon nanotubes are substantially parallel to theaxis of the untwisted carbon nanotube wire. More specifically, theuntwisted carbon nanotube wire includes a plurality of successive carbonnanotube segments joined end to end by van der Waals attractive forcetherebetween. Each carbon nanotube segment includes a plurality ofcarbon nanotubes substantially parallel to each other, and combined byvan der Waals attractive force therebetween. The carbon nanotubesegments can vary in width, thickness, uniformity, and shape. The lengthof the untwisted carbon nanotube wire can be arbitrarily set as desired.A diameter of the untwisted carbon nanotube wire ranges from about 0.5nanometers to about 100 micrometers.

The twisted carbon nanotube wire can be formed by twisting a drawncarbon nanotube film using a mechanical force to turn the two ends ofthe drawn carbon nanotube film in opposite directions. Referring to FIG.5, the twisted carbon nanotube wire includes a plurality of carbonnanotubes helically oriented around an axial direction of the twistedcarbon nanotube wire. More specifically, the twisted carbon nanotubewire includes a plurality of successive carbon nanotube segments joinedend to end by van der Waals attractive force therebetween. Each carbonnanotube segment includes a plurality of carbon nanotubes parallel toeach other, and combined by van der Waals attractive force therebetween.The length of the carbon nanotube wire can be set as desired. A diameterof the twisted carbon nanotube wire can be from about 0.5 nanometers toabout 100 micrometers. Further, the twisted carbon nanotube wire can betreated with a volatile organic solvent after being twisted to bundlethe adjacent paralleled carbon nanotubes together. The specific surfacearea of the twisted carbon nanotube wire will decrease, while thedensity and strength of the twisted carbon nanotube wire will increase.

In step (S11), carbon nanotube composite structure 110 can be made byapplying a protective layer 114 on a surface of the carbon nanotubestructure 112. The carbon nanotube structure 112 can be suspended in adepositing chamber during depositing the protective layer 114 so thattwo opposite surfaces of the carbon nanotube structure 112 are coatedwith the protective layer 114. In some embodiments, each of theplurality of carbon nanotubes is fully enclosed by the protective layer114. In one embodiment, the carbon nanotube structure 112 is located ona frame so that the middle portion of the carbon nanotube structure 112is suspended through the through hole of the frame. The frame can be anyshape, such as a quadrilateral. The carbon nanotube structure 112 canalso be suspended by a metal mesh or metal ring.

The method of depositing the protective layer 114 can be physical vapordeposition (PVD), chemical vapor deposition (CVD), atomic layerdeposition, magnetron sputtering, or spraying.

The plurality of openings 116 are formed because of the plurality ofapertures of the carbon nanotube structure 112. The plurality ofopenings 116 and the plurality of apertures have the same shape anddifferent size. The size of the plurality of openings 116 is smallerthan that of the plurality of apertures because the protective layer 114is deposited in the plurality of apertures.

The thickness of the protective layer 114 is in a range from about 3nanometers to about 50 nanometers. In one embodiment, the thickness ofthe protective layer 114 is in a range from about 3 nanometers to about20 nanometers. If the thickness of the protective layer 114 is less than3 nanometers, the protective layer 114 cannot prevent the carbonnanotubes from being destroyed in following etching process. If thethickness of the protective layer 114 is greater than 50 nanometers, theplurality of apertures may be fully filled by the protective layer 114and the plurality of openings 116 cannot be obtained.

The material of the protective layer 114 can be metal, metal oxide,metal nitride, metal carbide, metal sulfide, silicon oxide, siliconnitride, or silicon carbide. The metal can be gold, nickel, titanium,iron, aluminum, titanium, chromium, or alloy thereof. The metal oxidecan be alumina, magnesium oxide, zinc oxide, or hafnium oxide. Thematerial of the protective layer 114 is not limited above and can be anymaterial as long as the material can be deposited on the carbon nanotubestructure 112, would not react with the carbon nanotubes and would notbe etched easily in following drying etching process. The protectivelayer 114 is combined with the carbon nanotube structure 112 by van derWaals attractive force therebetween only.

As shown in FIG. 6, in one embodiment, an alumina layer of 10 nanometersthickness is deposited on two stacked drawn carbon nanotube films byelectron beam evaporation. The aligned direction of the carbon nanotubesbetween adjacent stacked drawn carbon nanotube films is 90 degrees. Asshown in FIG. 7, the alumina layer cover entire surface of each carbonnanotube.

Furthermore, a step of scanning the carbon nanotube structure 112 alongthe length direction of the carbon nanotubes of the carbon nanotubestructure 112 can be performed before the applying the protective layer114 on the surface of the carbon nanotube structure 112. When the carbonnanotube structure 112 is a drawn carbon nanotube film, the drawn carbonnanotube film is irradiated by a laser device in an atmospherecomprising of oxygen therein. The power density of the laser is greaterthan 0.053×10¹² watts per square meter. The drawn carbon nanotube filmcan be heated by fixing the drawn carbon nanotube film and moving thelaser device at a substantially uniform speed to irradiate the drawncarbon nanotube film. When the laser irradiates the drawn carbonnanotube film, the laser is focused on the surface of the drawn carbonnanotube film to form a laser spot. The diameter of the laser spotranges from about 10 micrometers to about 100 micrometers. The laserscanning time is less than 1.8 seconds. In one embodiment, the laserdevice is carbon dioxide laser device. The power of the laser device isabout 30 watts. The wavelength of the laser is about 1.06 micrometers.The diameter of the laser spot is about 20 micrometers to about 80micrometers. The velocity of the laser movement is less than 10millimeters per second. The distance between two adjacent scanning pathsis in a range from about 0.05 millimeters to about 0.5 millimeters. Asshown in top half part of FIG. 8, after laser scanning, the drawn carbonnanotube film includes a plurality of carbon nanotube bundles spacedfrom each other. After the laser scanning, the drawn carbon nanotubefilm should still be free-standing. If the laser scanning cut throughthe drawn carbon nanotube film along laser scanning moving direction,the edges of the drawn carbon nanotube film should be fixed on a frame.When the carbon nanotube structure 112 includes two crossed drawn carbonnanotube films, the two drawn carbon nanotube films should be scannedrespectively and then stacked with each other.

In step (S12), the carbon nanotube composite structure 110 can be indirect contact with the surface of the metal layer 102 or suspendedabove the surface of the metal layer 102 by a support. In oneembodiment, the carbon nanotube composite structure 110 is transferredon the surface of the metal layer 102 through the frame above.

Furthermore, the placing the carbon nanotube composite structure 110 onthe metal layer 102 comprises solvent treating the substrate 100 withthe carbon nanotube composite structure 110 thereon. Because there isair between the carbon nanotube composite structure 110 and the metallayer 102, the solvent treating can remove the air therebetween andallow the carbon nanotube composite structure 110 to be in directcontact and firmly adhered on the surface of the metal layer 102. Thesolvent treating can be applying a solvent to entire surface of thecarbon nanotube composite structure 110 or immersing the entiresubstrate 100 with the carbon nanotube composite structure 110 in asolvent. The solvent can be water or volatile organic solvent (e.g.ethanol, methanol, acetone, dichloroethane, chloroform, or mixturesthereof). In one embodiment, the ethanol is applied on surface of thecarbon nanotube composite structure 110 and then the substrate 100 withthe carbon nanotube composite structure 110 is dried by natural airdrying.

In the step (S13), the dry etching can be plasma etching or reactive ionetching (RIE). In one embodiment, the dry etching is performed byapplying plasma energy on the entire or part surface of the metal layer102 via a plasma device. The plasma gas can be an inert gas and/or othergases suitable for etching, such as argon (Ar), helium (He), chlorine(Cl₂), hydrogen (H₂), oxygen (O₂), fluorocarbon (CF₄), ammonia (NH₃), orair.

In one embodiment, the plasma gas is a mixture of oxygen and argon. Thepower of the plasma device can be in a range from about 20 watts toabout 70 watts. The plasma flow of oxygen can be in a range from about 5standard-state cubic centimeters per minute (sccm) to about 20 sccm. Theplasma flow of argon can be in a range from about 15 sccm to about 25sccm. When the plasma is produced in vacuum, the work pressure of theplasma can be in a range from about 3 Pa to 10 Pa. The time for plasmaetching can be in a range from about 10 seconds to about 20 seconds.

In the plasma etching process, the plasma gas would react with theexposed portion of the metal layer 102 and would not react with theprotective layer 114, or reaction between the plasma gas and theprotective layer 114 is much slower than reaction between the plasma gasand the metal layer 102. Also, the plasma gas would not react with thesubstrate 100, or reaction between the plasma gas and the substrate 100is much slower than reaction between the plasma gas and the metal layer102. The selection relationship of the plasma gas, material of the metallayer 102 and material of the protective layer 114 is shown in Table 1below.

TABLE 1 number metal layer protective layer plasma gas 1 Al SiO₂ Cl₂ andBCl₃ 2 Au, Cr or Ni SiO₂, SiN_(x) or Al₂O₃ O₂ and Ar₂ 3 Cu SiO₂, SiN_(x)or Al₂O₃ SiCl₄ and Ar₂

In the etching process, the etching gas reacts with the metal layer 102,but does not react with the protective layer 114 or react with theprotective layer 114 at a speed much less than that of the reactionbetween the etching gas and the metal layer 102. Thus, the exposedportion of the metal layer 102 would be etched gradually and the portionof the metal layer 102 that are shielded by the carbon nanotubecomposite structure 110 would be remained.

The metal nanowire film 104 and the carbon nanotube composite structure110 substantially have the same pattern. The pattern of the metalnanowire film 104 depends on the pattern of the carbon nanotubecomposite structure 110. When the carbon nanotube structure 112 includesa plurality of carbon nanotubes parallel with each other, the metalnanowire film 104 includes a plurality of metal nanowires parallel witheach other. When the carbon nanotube structure 112 includes a pluralityof carbon nanotubes crossed with each other, the metal nanowire film 104includes a plurality of metal nanowires crossed with each other. Theintersections of the crossed metal nanowires are integrated.

The width of the metal nanowires can be less than 100 nanometers, suchas less than 50 nanometers. The distance between adjacent two metalnanowires can be in a range from about 10 nanometers to about 300nanometers, such as from about 20 nanometers to about 100 nanometers.The height of the metal nanowires is the same as the thickness of themetal layer 102. In one embodiment, the width of the metal nanowires isin a range from about 5 nanometers to about 20 nanometers, and thedistance between adjacent two metal nanowires is in a range from about 5nanometers to about 20 nanometers.

In step (S14), the method of removing the carbon nanotube compositestructure 110 can be ultrasonic method, or adhesive tape peeling,oxidation. In one embodiment, the substrate 100 with the carbon nanotubecomposite structure 110 thereon is placed in an N-methyl pyrrolidonesolution and ultrasonic treating for several minutes.

Different examples of the metal nanowire films, methods for making thesame and test results are described below.

Example 1

In example 1, two drawn carbon nanotube films are stacked with eachother and the aligned directions of the carbon nanotubes in the twoadjacent drawn carbon nanotube films are perpendicular with each otheras shown in FIG. 6. The edges of the two drawn carbon nanotube films arefixed on the metal frame so that the middle parts of the two drawncarbon nanotube films are suspended. The two drawn carbon nanotube filmsare coated with an alumina layer with a thickness of 10 nanometers, byelectron beam evaporation so as to obtain the carbon nanotube compositestructure 110. A gold film is deposited on entire surface of the glassplate substrate 100 to form the metal layer 102. The thickness of thegold film is respectively 10 nanometers, 15 nanometers, 20 nanometers,25 nanometers. The carbon nanotube composite structure 110 is placed onand in direct contact with the gold film through the metal frame. Thegold film is dry etched by plasma gas of oxygen and argon to form themetal nanowire film 104. The power of the plasma device is 40 watts. Theplasma flow of oxygen is 7 sccm. The plasma flow of argon is 20 sccm.When the plasma is produced in vacuum, the work pressure of the plasmais 5 Pa. The time for plasma etching is 15 seconds. The glass plate isplaced in an N-methyl pyrrolidone solution and ultrasonic treating forseveral minutes to remove the two drawn carbon nanotube films.

As shown in FIG. 6 and FIG. 9, the metal nanowire film 104 and thecarbon nanotube composite structure 110 substantially have the samepattern. As shown in FIGS. 9-11, the metal nanowire film 104 includes aplurality of first metal nanowires substantially arranged along the samefirst direction and a plurality of second metal nanowires substantiallyarranged along the same second direction substantially perpendicularwith the first direction. The width of the metal nanowires is 20nanometers. The distance between adjacent two metal nanowires is 50nanometers. The height of the metal nanowires is the same as thethickness of the gold metal layer 102. As shown in FIG. 12, test resultsof transmittance for visible light and sheet resistance of the metalnanowire film 104 fabricated in example 1 are given. As the thickness ofthe gold metal layer 102 increases, namely, the height of the metalnanowires increases, the transmittance for visible light of the metalnanowire film 104 decreases. When the thickness of the gold metal layer102 is respectively 10 nanometers, 15 nanometers, 20 nanometers, 25nanometers, the transmittance for visible light of the metal nanowirefilm 104 is respectively 76%, 68%, 61%, and 53%. As the thickness of thegold metal layer 102 increases, the sheet resistance of the metalnanowire film 104 decreases. When the thickness of the gold metal layer102 is respectively 10 nanometers, 15 nanometers, 20 nanometers, 25nanometers, the sheet resistance of the metal nanowire film 104 isrespectively 21.2Ω·□⁻¹ (Ohms per square), 8.8Ω·□⁻¹, 6.2Ω·□⁻¹ and3.9Ω·□⁻¹.

Example 2

In example 2, the method for making the metal nanowire film 104 issimilar to the method of example 1 except that a single drawn carbonnanotube film is scanned by laser, coated with alumina layer and thenfixed on the metal frame to form the carbon nanotube composite structure110. The scanning path is along the length direction of the carbonnanotubes of the drawn carbon nanotube film. The wavelength of the laseris about 1.06 micrometers. The distance between two adjacent scanningpaths is 0.1 millimeters. The thickness of the gold metal layer 102 is10 nanometers.

As shown in FIG. 13-15, the metal nanowire film 104 includes a pluralityof metal nanowires bundles 106 parallel with and spaced from each other.Each of the plurality of metal nanowires bundles 106 includes aplurality of first metal nanowires 107 parallel with each other. Each ofthe plurality of metal nanowires bundles 106 also includes a pluralityof randomly arranged second metal nanowires 108 dispersed on the surfaceof and in contact with adjacent some of the plurality of first metalnanowires 107. The distance between adjacent two first metal nanowires107 is less than the distance between adjacent two metal nanowiresbundles 106. The plurality of first metal nanowires 107 are notabsolutely form a direct line and extend along the axial direction, someof them may be curved and in contact with each other. Some variationscan occur in the metal nanowire film 104. The distance between adjacenttwo first metal nanowires 107 can be in a range from about 0 nanometersto about 50 nanometers. The distance between adjacent two metalnanowires bundles 106 can be in a range from about 10 micrometers toabout 100 micrometers. The width of the metal nanowires bundles 106 canbe in a range from about 50 micrometers to about 500 micrometers. Thewidth of the metal nanowires 107, 108 can be in a range from about 0.5nanometers to about 50 nanometers. The distance between adjacent twometal nanowires bundles 106 depends on the diameter of the laser spot.The width of the metal nanowires bundles 106 depends on the distancebetween two adjacent laser scanning paths. The width of the metalnanowires 107, 108 depends on the diameter of the carbon nanotubes ofthe drawn carbon nanotube film. The height of the metal nanowires 107,108 depends on the thickness of the gold metal layer 102.

Example 3

In example 3, the method for making the metal nanowire film 104 issimilar to the method of example 1 except that two drawn carbon nanotubefilms are scanned by laser, coated with alumina layer and then fixed onthe metal frame to form the carbon nanotube composite structure 110. Thescanning path is along the length direction of the carbon nanotubes ofeach of the drawn carbon nanotube films. The wavelength of the laser isabout 1.06 micrometers. The distance between two adjacent scanning pathsis 0.1 millimeters. The thickness of the gold metal layer 102 isrespectively 10 nanometers, 15 nanometers, 20 nanometers, 25 nanometers.

As shown in FIGS. 16-17, the metal nanowire film 104 includes aplurality of first metal nanowires bundles 106 parallel with, spacedfrom each other and extend along the same first direction a plurality ofsecond metal nanowires bundles 106 parallel with, spaced from each otherand extend along the same second direction substantially perpendicularwith the first direction. The metal nanowire film 104 is a metal mesh.As shown in FIG. 18, when the thickness of the gold metal layer 102 isrespectively 10 nanometers, 15 nanometers, 20 nanometers, 25 nanometers,the transmittance for visible light of the metal nanowire film 104 isrespectively 87.5%, 82.6%, 71.7%, and 59.4%, the sheet resistance of themetal nanowire film 104 is respectively 78.2Ω·□⁻¹, 50.9Ω·□⁻¹, 18.6Ω·□⁻¹and 11.5Ω·□⁻¹. Compare with FIG. 13, it is shown that after the laserscanning, when the thickness of the gold metal layer 102 is the same,the transmittance for visible light of the metal nanowire film 104increases, and the sheet resistance of the metal nanowire film 104 alsoincreases.

Example 4

In example 4, the method for making the metal nanowire film 104 issimilar to the method of example 1 except that the substrate 100 is aPET film. The thickness of the gold metal layer 102 is 15 nanometers. Asshown in FIG. 19, the sheet resistance under 120° C. of the metalnanowire film 104 is substantially stable and maintains as 50Ω·□⁻¹. Asshown in FIG. 20, the sheet resistance of the metal nanowire film 104 issubstantially stable and unchanged under the temperature from about 40°C. to about 120° C.

Example 5

In example 5, the method for making the metal nanowire film 104 issimilar to the method of example 1 except that the metal layer 102 is analuminum film. The thickness of the aluminum metal layer 102 isrespectively 10 nanometers, 15 nanometers, 20 nanometers, 25 nanometers.The SEM image of the aluminum metal nanowire film 104 is shown in FIG.21. The test results of transmittance and sheet resistance of thealuminum metal nanowire film 104 is shown in FIG. 22.

Example 6

In example 6, the method for making the metal nanowire film 104 issimilar to the method of example 1 except that the metal layer 102 is acopper film. The thickness of the copper metal layer 102 is respectively10 nanometers, 15 nanometers, 20 nanometers, 25 nanometers. The SEMimage of the copper metal nanowire film 104 is shown in FIG. 23. Thetest results of transmittance and sheet resistance of the copper metalnanowire film 104 is shown in FIG. 24.

Example 7

In example 7, the method for making the metal nanowire film 104 issimilar to the method of example 3 except that the metal layer 102 is analuminum film. The thickness of the aluminum metal layer 102 isrespectively 10 nanometers, 15 nanometers, 20 nanometers, 25 nanometers.The SEM image of the aluminum metal nanowire film 104 is shown in FIG.25. The test results of transmittance and sheet resistance of thealuminum metal nanowire film 104 is shown in FIG. 26.

Example 8

In example 8, the method for making the metal nanowire film 104 issimilar to the method of example 3 except that the metal layer 102 is acopper film. The thickness of the copper metal layer 102 is respectively10 nanometers, 15 nanometers, 20 nanometers, 25 nanometers. The SEMimage of the copper metal nanowire film 104 is shown in FIG. 27. Thetest results of transmittance and sheet resistance of the copper metalnanowire film 104 is shown in FIG. 28.

Example 9

In example 9, the method for making the metal nanowire film 104 issimilar to the method of example 4 except that the metal layer 102 is analuminum film. FIG. 29 shows a relationship of sheet resistance underheating and temperature of the metal nanowire film 104 fabricated inexample 9. FIG. 30 shows a relationship of sheet resistance underheating and time of the metal nanowire film 104 fabricated in example 9.

Example 10

In example 10, the method for making the metal nanowire film 104 issimilar to the method of example 4 except that the metal layer 102 is acopper film. FIG. 31 shows a relationship of sheet resistance underheating and temperature of the metal nanowire film 104 fabricated inexample 10. FIG. 32 shows a relationship of sheet resistance underheating and time of the metal nanowire film 104 fabricated in example10.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, including inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including, the fullextent established by the broad general meaning of the terms used in theclaims.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. The description and the claims drawn to a method may includesome indication in reference to certain steps. However, the indicationused is only to be viewed for identification purposes and not as asuggestion as to an order for the steps.

What is claimed is:
 1. A method for making a metal nanowire film, themethod comprising: providing a substrate having a first surface, andapplying a metal layer on the first surface, wherein the metal layer hasa metal layer surface spaced from the first surface; providing a carbonnanotube composite structure, wherein the carbon nanotube compositestructure defines a plurality of openings and comprises a carbonnanotube structure and a protective layer, coated on the carbon nanotubestructure; and the carbon nanotube structure comprises a plurality ofcarbon nanotubes arranged substantially along the same direction;placing the carbon nanotube composite structure on the metal layersurface, wherein parts of the metal layer are exposed by the pluralityof openings; dry etching the metal layer using the carbon nanotubecomposite structure as a mask; and removing the carbon nanotubecomposite structure.
 2. The method of claim 1, wherein the carbonnanotube structure comprises a first carbon nanotube film and a secondcarbon nanotube film stacked with each other.
 3. The method of claim 2,wherein the first carbon nanotube film comprises a plurality of firstcarbon nanotubes that are joined end-to-end by van der Waals attractiveforce therebetween and substantially arranged along the same firstdirection; the second carbon nanotube film comprises a plurality ofsecond carbon nanotubes that are joined end-to-end by van der Waalsattractive force therebetween and substantially arranged along the samesecond direction; and the second direction is different from the firstdirection.
 4. The method of claim 1, wherein the carbon nanotubestructure comprises a plurality of carbon nanotube wires parallel withand spaced from each other.
 5. The method of claim 1, wherein theproviding the carbon nanotube composite structure comprises suspendingthe carbon nanotube structure and applying the protective layer on thecarbon nanotube structure.
 6. The method of claim 5, wherein each of theplurality of carbon nanotubes is fully enclosed by the protective layer.7. The method of claim 5, wherein the providing the carbon nanotubecomposite structure further comprises scanning the carbon nanotubestructure along a length direction of the plurality of carbon nanotubesby a laser.
 8. The method of claim 7, wherein a power density of thelaser is greater than 0.053×10¹² watts per square meter; the laser isfocused on the carbon nanotube structure to form a laser spot, adiameter of the laser spot is in a range from about 10 micrometers toabout 100 micrometers.
 9. The method of claim 1, wherein a thickness ofthe protective layer is in a range from about 3 nanometers to about 50nanometers.
 10. The method of claim 9, wherein the thickness of theprotective layer is in a range from about 3 nanometers to about 20nanometers.
 11. The method of claim 1, wherein the protective layercomprises a material selected from the group consisting of metal, metaloxide, metal nitride, metal carbide, metal sulfide, silicon oxide,silicon nitride, and silicon carbide.
 12. The method of claim 1, whereinthe dry etching is plasma etching or reactive ion etching.
 13. Themethod of claim 1, wherein the removing the carbon nanotube compositestructure comprises ultrasonic treating, adhesive tape peeling, oroxidation.
 14. The method of claim 1, wherein the substrate comprisesmaterial selected from the group consisting of silicon wafer, ceramic,glass, quartz, diamond, metal oxide, and polymer.
 15. The method ofclaim 1, wherein a material of the metal layer is elected from the groupconsisting of gold, silver, copper, iron, aluminum, nickel or chromium.